This invention relates to novel organofunctional silanes and their use in binding agent compositions for foundry sands. More particularly, this invention relates to organofunctional silanes that contain at least one hindered alkoxy group and its use in binding agent compositions having especially good shelf life.
It is well known in the art that one can impart general improved strengths and increased humidity resistance to foundry cores by adding a silane compound to the resinous foundry binder used to form the cores. Foundry cores made with such resinous binders as phenolic/isocyanate systems, furan systems, oil modified polyol/polyisocyanate systems, phenolic resins and urea/phenolic resins have a tendency to lose strength and become weak upon exposure to humid conditions. As illustrated by U.S. Pat. Nos. 3,409,579 and 3,403,721, silane compounds have been added to such resinous binders to increase the humidity resistance and general strength of foundry cores made with these binders. Aqueous dispersions of silane compounds have also been used as binders themselves (see U.S. Pat. No. 3,093,494).
It is known that aminoalkyl trialkoxysilanes, such as -aminopropyltrimethoxysilane, improve the adherence of thermosetting resins to inorganic oxide materials. It is furthermore known that these amino-silanes can be mixed with thermosetting phenolic resins and then the resulting mixtures can be mixed directly with sands or other inorganic oxide material to be shaped and solidified (cf. DE-AS No. 1,252,853 and DE-PS No. 1,494,381).
The use of N-(aminoalkyl)-aminoalkylsilanes as adhesion improvers between thermosetting resins and inorganic oxide material is also known. These compounds are used in the same manner as the above-mentioned aminosilanes in which there is no substitution on the nitrogen atom (cf. U.S. Pat. No. 3,234,159).
Both the aminoalkylsilanes which are not substituted on the nitrogen atom and those which are substituted by aminoalkyl groups, all of which are referred to hereinafter as aminosilanes, improve the adhesion of thermosetting phenolic resins to inorganic oxide substances to virtually the same degree when they are mixed with the resins. This improvement of adhesion, however, diminishes in the course of time if these aminosilane-containing resins are stored for a relatively long time at room temperature. U.S. Pat. No. 4,256,623 reports that, after standing for only 14 days, for example, the adhesion-improving action of aminosilanes declines by about 40%, and at the end of only a month the adhesivizing effect produced by 3-aminopropyltriethyxysilane in phenolic resin has been reduced by one half.
It has been further reported that the loss of the adhesivizing action of the aminosilanes in mixture with thermosetting resins is probably due to a decomposition of these silanes in the resins. Therefore, there existed the problem of finding an adhesivizing agent which, when mixed with thermosetting resins, decomposes very slightly or not at all, and produces its adhesivizing action to the same or an only slightly lesser extent, even after the resin has been stored for a relatively long time and which therefore will be useful in the preparation of binding agents for inorganic oxide materials such as, for example, foundry sands, such binding agents being made from ureido-functional silanated phenolic resins whose strength enhancing effectiveness will remain unaltered or only slightly reduced, even after a relatively long period of storage.
U.S. Pat. Nos. 3,671,562; 3,754,971 and 4,046,794 disclose ureido-functional organosilicon compounds and the use of same as coupling agents on inorganic substrates such as glass, clay, silica, hydrated silica, fumed silica, sand, e.g., foundry sand and the like. U.S. patent application No. 309,657 filed Oct. 8, 1981 described ureido-functional organosilicon compounds having two hydrolyzable or hydroxy groups and in which at least one ureido-functional group is connected to silicon by groups containing at least five carbon atoms which are also useful as binding agents.
Despite repeated advances in the art there continues to remain the need to seek out and identify novel materials useful as binding agents which will impart good shelf life to the composition. It is believed that this invention fulfills this task and represents an advance over the existing art.